The field of the present invention is transmissions for auxiliary equipment on variable speed engines.
Conventionally, powered accessories such as alternators, air conditioning pumps, power steering pumps and the like for an automobile or other vehicle have been driven from one end of the crankshaft by means of belts and pulleys. Such systems have resulted in the accessories being driven at velocities which are proportional to the rotating speed of the engine. Typically, an automobile engine will vary greatly in its operating speed range. Thus, the accessories have been required to operate over a wide range of speeds. At the low end or idle range for the engine, the driven speeds of the accessories may be considered marginally low while at the upper end of the engine speed range, the accessories are being driven needlessly fast.
It is desirable that the speed range of the accessories normally driven by an engine be rotated at a more uniform rate. By doing so, the accessories may operate more efficiently, useless power is not drained from the engine, greater reliability may be obtained and noise reduced. Additionally, with a limited speed range, certain of the accessories may be reduced in size and strength resulting in a savings of cost and power through smaller, lighter components.
To overcome the foregoing difficulties, devices have been developed which provide for some speed control. In the area of multiple fixed ratio transmissions, planetary gearing has been employed to provide speed reduction while direct drive through some clutching means provides a selectable second ratio. In the area of continuously variable ratios, variable diameter pulley mechanisms have been employed. Such systems are often needlessly complicated or provide a relatively weak or short lived clutching mechanism associated with at least one of the ratio modes.